Power supply device, vehicle in which same is used, and bus bar

ABSTRACT

A plurality of battery cells each having a positive electrode terminal and a negative electrode terminal; and a bus bar which connects the electrode terminals facing each other in the battery cells adjacently disposed among the plurality of battery cells.

TECHNICAL FIELD

The present invention relates to a power supply device, a vehicle usingthe same, and a bus bar for electrically connecting battery cells usedin the power supply device.

BACKGROUND ART

A power supply device using a secondary battery has been used for apower supply for driving a vehicle, for example. The power supply devicementioned above is provided with a plurality of battery cells 501, aplurality of insulating separators 518, a pair of bind bars 515, and apair of end plates 514, as illustrated in an exploded perspective viewin FIG. 5. Each of insulating separators 518 is interposed betweenadjacent battery cells 501. Battery cells 501 and insulating separators518 are stacked in an alternating fashion to form battery stacked body599. Both end faces of battery stacked body 599 in the stackingdirection of battery cells 501 are respectively covered by end plates514. Respective bind bars 515 extend along the stacking direction ofbattery cells 501, and are fixed to end plates 514 on both ends ofbattery stacked body 599. In the power supply device mentioned above,electrode terminals 502 of battery cells 501 are electrically connectedeach other through bus bars 540. The bus bar 540 is configured of metalboard having excellent conductivity.

Since members of the battery cells or the like constituting the powersupply device include manufacturing allowance, distances between theelectrode terminals adjacently disposed are not necessarily constant,and therefore it is necessary to absorb dispersion of these. Further, ina case where the power supply device receives outer force, it happensthat the battery cells adjacently disposed are relatively misaligned. Inthis case, in order to absorb the misalignment through the bus bar, itis required that the bus bar has flexibility capable of beingresiliently deformed.

As the way where the bus bar has flexibility, the bus bar in whichbending processing is carried out, has been known (refer to PatentLiterature 1, for example). However, in the conventional configuration,the bent portion for buffering stress is disposed between two connectionparts connected to the electrode terminals. In this shape, in a casewhere size between terminals of adjacent cells is short, there is aproblem that forming the bus bar (press working) becomes difficult.

Recently, as a battery cell, a lithium ion secondary battery of highcapacity has been spread. In this lithium ion secondary battery,generally, the positive electrode is made of aluminum, and the negativeelectrode is made of copper. When these lithium ion secondary batteriesare connected each other in series by the bus bars, it is necessary,that the positive electrode made of aluminum in one of the lithium ionsecondary batteries, is connected to the negative electrode made ofcopper in another of the lithium ion secondary batteries by the busbars.

When different kinds of metals are joined each other by laser welding,the intermetallic compound is made, and then the mechanical strength atthe joining portion is decreased. Therefore, the following bus bar isused (for example, refer to Patent Literature 2). The bus bar is made ofa clad material which is joined by specially rolling the copper plateand aluminum plate. By using this clad material as a bus bar, aluminumplates are contacted in the positive electrode, and copper plates arecontacted, to prevent the intermetallic compound from being made. Then,laser welding of the high reliability can be obtained. However, there isa problem that the bus bar made of the clad material is expensive.

CITATION LIST Patent Literature

-   PTL 1: Unexamined Japanese Patent Publication No. 2013-197017-   PTL 2: Unexamined Japanese Patent Publication No. 2014-229483

SUMMARY OF THE INVENTION

The present invention has been made in view of the above background. Anobject of the present invention is to supply a power supply device, avehicle using the same, and a bus bar, which enhance the joiningstrength between a bus bar and battery cells, and improve reliability.

According to a power supply device relating to a first aspect of thepresent invention, the power supply device include: a plurality ofbattery cells each having a positive electrode terminal and a negativeelectrode terminal; and a bus bar which connects the electrode terminalsfacing each other in the battery cells adjacently disposed among theplurality of battery cells. The bus bar includes: a first connectionportion which is connected to the electrode terminal of one of thebattery cells; a second connection portion which is connected to theelectrode terminal of another of the battery cells, is disposedsubstantially in parallel to the first connection portion; a firstintermediate portion which is continuous from the first connectionportion through a first bending portion that is bent from the firstconnection portion, is disposed substantially in parallel to the firstconnection portion; and a second intermediate portion which iscontinuous from the second connection portion through a second bendingportion that is bent from the second connection portion, is disposedsubstantially in parallel to the second connection portion. The firstintermediate portion and the second intermediate portion are connectedin a continuous manner by a third bending portion having a U-shapedcross-section. According to the above configuration, the firstconnection portion and the second connection portion are connectedthrough three portions of the first bending portion, the second bendingportion, and the third bending portion, and then by deforming of these,the displacement of positional relation between the first connectionportion and the second connection portion can be absorbed. Whileabsorbing displacement between the battery cells, the electricalconnecting state can be maintained, and then the reliability of thepower supply device can be improved.

According to the power supply device relating to a second aspect, anarea of the second intermediate portion is larger than an area of thefirst intermediate portion, and a connecting cutout for connecting aterminal is formed at the second intermediate portion.

According to the power supply device relating to a third aspect, theconnecting cutout is a connecting hole which is opened at the secondintermediate portion.

According to the power supply device relating to a fourth aspect, theconnecting hole has a circular shape.

According to the power supply device relating to a fifth aspect, thepositive electrode terminal and the negative electrode terminal are madeof different kinds of metals, the metal of the bus bar is the same kindof the metal as one of the different kinds of metals, and one of thefirst connection portion and the second connection portion, connected tothe electrode terminal having the same kind of the metal, partially hasa narrow area having a width narrower than that of the other of thefirst connection portion and the second connection portion. According tothe above configuration, the area continued to the joining surface ofsame metal contact, is strong in joining strength at a time of laserwelding. The area continued to the joining surface of different metalcontact, is weak in joining strength. As the area of same metal contactis narrower than the area of different metal contact, a difference ofjoining strength between the positive and negative electrode terminalcan be suppressed.

According to the power supply device relating to a sixth aspect, thefirst connection portion and the second connection portion eachpartially have a thin area whose thickness is thin.

According to the power supply device relating to a seventh aspect, thebus bar is one sheet of a bended metal board. According to the aboveconfiguration, without an expensive clad material, the bus bar can bemade of one sheet of the metal board integrally, to largely reducecosts.

According to the power supply device relating to an eighth aspect, asurface of the electrode terminal is plated with a plating metaldifferent from the electrode terminal.

According to the power supply device relating to a ninth aspect, theelectrode terminal is made of copper, the plating metal is nickel, thebus bar is made of aluminum.

A vehicle relating to a tenth aspect, has any one of the above powersupply devices.

According to a bus bar relating to an eleven aspect, A bus bar forconnecting electrode terminals of a pair of battery cells, includes: afirst connection portion which is connected to the electrode terminal ofone of the battery cells; a second connection portion which is connectedto the electrode terminal of another of the battery cells, is disposedsubstantially in parallel to the first connection portion; a firstintermediate portion which is continuous from the first connectionportion through a first bending portion that is bent from the firstconnection portion, is disposed substantially in parallel to the firstconnection portion; and a second intermediate portion which iscontinuous from the second connection portion through a second bendingportion that is bent from the second connection portion, is disposedsubstantially in parallel to the second connection portion. The firstintermediate portion and the second intermediate portion are connectedin a continuous manner by a third bending portion having a U-shapedcross-section. According to the above configuration, the firstconnection portion and the second connection portion are connectedthrough three portions of the first bending portion, the second bendingportion, and the third bending portion, and then by deforming of these,the displacement of positional relation between the first connectionportion and the second connection portion can be absorbed. Whileabsorbing displacement between the battery cells, the electricalconnecting state can be maintained, and then the reliability of thepower supply device can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a power supply device according to oneexemplary embodiment of the present invention.

FIG. 2 is a schematic perspective view illustrating a connectingstructure of battery cells and bus bars of the power supply deviceillustrated in FIG. 1.

FIG. 3 is an exploded perspective view illustrating the connectingstructure of the battery cells and the bus bars illustrated in FIG. 2.

FIG. 4 is a perspective view illustrating the bus bars of FIG. 3.

FIG. 5 is an exploded perspective view illustrating a connecting statebetween electrode terminals and conventional bus bars.

FIG. 6 is an enlarged plan view illustrating one example of a firstconnection portion of the bus bar.

FIG. 7 is a plan view illustrating a battery stacked body of acomparative example.

FIG. 8 is a perspective view illustrating a state where a jig pressesthe bus bar of FIG. 7.

FIG. 9 is a sectional view illustrating a state where the jig of FIG. 8has pressed the bus bar.

FIG. 10 is an enlarged plan view illustrating an area which is pressedby the jig in the bus bar of FIG. 7.

FIG. 11 is a perspective view illustrating a state where a jig pressesthe bus bar of FIG. 6.

FIG. 12 is an enlarged plan view illustrating a first connection portionof a bus bar in a modified example.

FIG. 13 is an enlarged plan view illustrating a first connection portionof a bus bar in another modified example.

FIG. 14 is an enlarged plan view illustrating one example of a laserwelding pattern in the bus bar of FIG. 6.

FIG. 15 is an enlarged plan view illustrating one example of a laserwelding pattern in the bus bar of FIG. 12.

FIG. 16 is an enlarged plan view illustrating another example of a laserwelding pattern.

FIG. 17 is an enlarged plan view illustrating further another example ofa laser welding pattern.

FIG. 18 is a block diagram showing an example in which a power supplydevice is mounted on a hybrid car driven by both an engine and a motor.

FIG. 19 is a block diagram showing an example in which a power supplydevice is mounted in an electric car traveling only by a motor.

DESCRIPTION OF EMBODIMENT

An exemplary embodiment of the present invention is described below withreference to the drawings. However, the exemplary embodiment describedbelow shows an example of the present invention, and the battery pack ofthe present invention is not limited to the following. Further, in thepresent description, components shown in the scope of claims are notlimited to the components of the exemplary embodiment. Furthermore, inthe following description, the same names or the same reference marksdenote the same components or same type components, and detaileddescription is appropriately omitted. Further, regarding the elementsconstituting the present invention, a plurality of elements may beformed of the same component, and one component may serve as theplurality of elements. To the contrary, the function of one componentmay be shared by the plurality of components.

The power supply device of the present invention is used for variouspurposes, such as a power supply mounted on a powered vehicle such as ahybrid vehicle or an electric vehicle for supplying power to a travelmotor, a power supply for storing power generated by natural energy suchas photovoltaic power generation or wind-power generation, or a powersupply for storing night power, and are particularly used as a powersupply preferable for large power and large current.

In a power supply device shown in FIG. 1, a plurality of battery cells 1are fixed in a stacked state where each of insulating separators 18 isinterposed between the plurality of battery cells 1 and battery cells 1are insulated each other. In FIG. 1, as one example of battery cell 1,battery cell 1 is a rectangular parallelepiped battery (prismaticbattery). Battery cell 1 is a lithium ion secondary battery or the like.However, in the power supply device according to the present invention,the battery cell is not limited to the rectangular parallelepipedbattery, the lithium ion secondary battery. As the battery cell, anyother batteries which can be charged can also be used, such as anon-aqueous electrolyte secondary battery or a nickel-hydrogen batterycell other than the lithium ion secondary battery.

(Rectangular Battery)

As illustrated in FIGS. 2 and 3, battery cell 1 of the rectangularbattery is provided with positive and negative electrode terminals 2fixed on sealing plate 12 through insulating member 11. In FIGS. 2 and3, in order to simply explain the connecting state between battery cells1 and bus bars 40, insulating separators 18 stacked between batterycells 1 are omitted. Bus bar holder 20 (shown in FIG. 1, explained belowin detail) which disposes bus bars 40 in a fixed position, is alsoomitted. Each of positive and negative electrode terminals 2 includes aterminal base having joining surface 2B, and projecting portion 2Aprojecting from joining surface 2B. Joining surface 2B is plane inparallel with a surface of sealing plate 12. Further, projecting portion2A is provided at a center of this Joining surface 2B. Electrodeterminal 2 shown in FIG. 3, has a cylindrical shape of projectingportion 2A. Here, the projecting portion is not necessarily of thecylindrical shape, but may be of a polygonal column shape or an ellipticcylinder shape.

Stacked battery cells 1 is a rectangular parallelepiped of battery block16 which is fixed in a predetermined position by fixing parts 13. Fixingparts 13 includes a pair of end plates 14 disposed on both end faces ofstacked battery cells 1 and binding members 15 that fixes stackedbattery cells 1 in a pressurized state with both ends being fixed to endplates 4.

In battery block 16, battery cells 1 are stacked such that the surfaceshaving electrode terminals 2 of battery cells 1, that is, sealing plates12 in FIG. 2, are disposed in the same plane. In the power supply deviceshown in FIGS. 1 and 2, positive and negative electrode terminals 2 aredisposed on the upper surface of battery block 16. In battery block 16,battery cells 1 are stacked in a state where positive and negativeelectrode terminals 2 at both end portions of sealing plates 12 arehorizontally reversed. As shown in FIG. 3, adjacent electrode terminals2 are coupled by bus bars 40 of metal boards at both sides of batteryblock 16, and thereby battery cells 1 are electrically connected inseries.

Both end portions of bus bars 40 are connected to positive and negativeelectrode terminals 2, and thereby battery cells 1 are electricallyconnected in series or in parallel. The power supply device obtained byconnecting battery cells 1 in series can increase an output voltage. Thepower supply device obtained by connecting battery cells 1 in series andparallel can increase an output voltage and an output current.

Bus bar 40 has positioning portions which can guide on electrodeterminals 2. Bus bars 40 shown in FIGS. 2 and 3 each have open windows62 at both ends thereof as the positioning portion. Projecting portion2A of electrode terminal 2 in adjacently disposed battery cell 1 isguided into each of open windows 62. Bus bars 40 shown in FIGS. 2 and 3each have open windows 62 of through holes, and then projecting portion2A is inserted into open window 62. Open window 62 has an inner diameterwhich can guide projecting portion 2A of electrode terminal 2. Also, thepositioning portion of the bus bar is not limited to the through hole.Then, any shape which can position the bus bar by using projectingportion 2A of electrode terminal 2, can be available. As not shown inthe figures, for example, the positioning portion can be a cutoutportion where the bus bar is partially cut out.

(Bus Bar Holder 20)

Bus bars 40 are disposed at the fixed location by bus bar holders 20shown in FIG. 1, and guide projecting portions 2A of electrode terminal2 into open windows 62. Bus bar holder 20 is molded and made ofinsulating material of plastic or the like, and disposes bus bars 40 atthe fixed location. Bus bar holder 20 is coupled to battery block 16,and disposes bus bars 40 at the fixed location. Bus bar holder 20 iscoupled to insulating separator 18 stacked between the rectangularbatteries, and then is disposed at the fixed position. Alternatively,bus bar holder 20 is coupled to the rectangular batteries, and then iscoupled at the fixed position. Bus bar holder 20 shown in FIG. 1includes holder body 20A frame-shaped which disposes the plurality ofbus bars 40 at the fixed location, cover plate 20B which closes theupper opening portion of holder body 20A. Holder body 20A is disposed onthe upper surface of battery block 16 in a state where the plurality ofbus bars 40 are disposed at the fixed location. Here, open windows 62 ofeach of bus bars 40 are disposed at projecting portions 2A of electrodeterminals 2. Further, in this state, the laser beam is irradiated fromthe upper opening portion of holder body 20A, bus bar 40 is welded toelectrode terminals 2. After all of bus bars 40 are welded to electrodeterminals 2, cover plate 20B closes the upper opening portion of holderbody 20A.

(Bus Bar 40)

The perspective view of bus bar 40 is shown in FIG. 4. This bus bar 40has first connection portion 41, second connection portion 51, andconnecting portion 49 which connects these. These portions areintegrally made by bending a metal board. Bus bar 40 is made of materialhaving excellent conductivity. Preferably, the material is aluminum,copper, or the like.

First connection portion 41 is connected to electrode terminal 2 (at theleft side in FIG. 3) of one of the battery cells. Second connectionportion 51 is connected to electrode terminal 2 (at the right side inFIG. 3) of another of the battery cells. First connection portion 41 andsecond connection portion 51 is adjacently disposed, substantially inparallel. Thereby, in a stacked battery cell assembly where the sealingplates are disposed in the same plane, adjacent electrode terminals 2can be connected each other. As shown in FIGS. 3 and 4, open windows 62are formed at first connection portion 41, second connection portion 51respectively.

(Connecting Portion 49)

First connection portion 41 and second connection portion 51 areconnected through connecting portion 49. Connecting portion 49 has firstbending portion 43, first intermediate portion 45, second bendingportion 53, second intermediate portion 55, and third bending portion47. First connection portion 41 and first intermediate portion 45 areconnected through first bending portion 43. Second connection portion 51and second intermediate portion 55 are connected through second bendingportion 53. First intermediate portion 45 and second intermediateportion 55 are connected through third bending portion 47.

(First Bending Portion 43)

First bending portion 43 is bended at first connection bending area 42from first connection portion 41, and is also bended at firstintermediate bending area 44 between first intermediate portion 45 andfirst bending portion 43. Preferably, first connection bending area 42between first bending portion 43 and first connection portion 41, isbended at a substantially right angle. Preferably, first intermediatebending area 44 between first bending portion 43 and first intermediateportion 45, is also bended at a substantially right angle. Then, firstconnection portion 41, first bending portion 43, and first intermediateportion 45, are formed in a step. These first connection portion 41,first bending portion 43, and first intermediate portion 45, are formedby bending a sheet of a metal board. Only first connection portion 41 isfixed to the battery cell. Then, first intermediate portion 45 is notfixed, and is floating against the battery cell. Therefore, even thougha distance between first connection portion 41 and first intermediateportion 45 changes relatively, first connection bending area 42 andfirst intermediate bending area 44 in first bending portion 43 aredeformed by their bending, and thereby this change can be absorbed.

(Second Bending Portion 53)

In the same way, second bending portion 53 is bended at secondconnection bending area 52 from second connection portion 51, and isalso bended at second intermediate bending area 54 between secondintermediate portion 55 and second bending portion 53. Preferably,second connection bending area 52 between second bending portion 53 andsecond connection portion 51, is bended at a substantially right angle.Preferably, second intermediate bending area 54 between second bendingportion 53 and second intermediate portion 55, is also bended at asubstantially right angle. Then, second connection portion 51, secondbending portion 53, and second intermediate portion 55, are formed in astep. These second connection portion 51, second bending portion 53, andsecond intermediate portion 55, are formed by bending a sheet of a metalboard. Second connection portion 51 side is fixed to the battery cell.Then, second intermediate portion 55 is not fixed. Therefore, eventhough a distance between second connection portion 51 and secondintermediate portion 55 changes relatively, this change can be absorbedby second connection bending area 52 and second intermediate bendingarea 54 in second bending portion 53.

(Third Bending Portion 47)

First intermediate portion 45 and second intermediate portion 55 areconnected through third bending portion 47. Concretely, firstintermediate portion 45 and third bending portion 47 are connectedthrough third intermediate bending area 46. Then, second intermediateportion 55 and third bending portion 47 are connected through fourthintermediate bending area 56. Preferably, third bending portion 47 isformed by bending the same metal board as first intermediate portion 45and second intermediate portion 55. Third bending portion 47 is formedin a U-shape in the vertical cross-section view. Therefore, by deformingin this portion, even though a distance between first intermediateportion 45 and second intermediate portion 55 changes relatively, thischange can be absorbed. The vertical cross-sectional shape of thirdbending portion 47 is not limited to the U-shape. For example, amountain-shape contrary to this can be available.

First intermediate portion 45 and second intermediate portion 55 aredisposed substantially in parallel. Second intermediate portion 55 andsecond connection portion 51 are disposed substantially in parallel.First intermediate portion 45 and second intermediate portion 55 aredisposed substantially in parallel, preferably in the same plane. Firstintermediate portion 45 has a rectangular shape in a plan view, andfirst connection bending area 42 and third intermediate bending area 46are provided at a substantially right angle, at the adjacent sidesthereof. In the same way, second intermediate portion 55 has arectangular shape in a plan view, and second connection bending area 52and fourth intermediate bending area 56 are provided at a substantiallyright angle, at the adjacent sides thereof. As this result, as shown inFIG. 4, even though a distance between first connection portion 41 andsecond connection portion 51 changes relatively in the X axis direction,this change can be absorbed by deforming of third bending portion 47.Even though positions of first connection portion 41 and secondconnection portion 51 changes relatively in the Y axis direction, thischange can be absorbed by deforming of first bending portion 43, secondbending portion 53. Even though positions of first connection portion 41and second connection portion 51 changes relatively in the Z axisdirection, this change can be absorbed by deforming of first bendingportion 43, second bending portion 53. In this way, even though arelative distance of first connection portion 41 and second connectionportion 51 changes in any of the XYZ axis directions, this change can beabsorbed by connecting portion 49 configured of first bending portion43, first intermediate portion 45, second bending portion 53, and secondintermediate portion 55. As mentioned above, in the exploded perspectiveview of FIG. 5, electrode terminals 502 are directly connected eachother by bus bars 540 each having a flat board shape. Compared with thisFIG. 5, the configuration of FIG. 4 can avoid problem of damage, break,or separation in the welding portion, which is caused by the loadapplied to the welding portion between electrode terminal 2 and bus bar40 by a relative displacement between first connection portion 41 andsecond connection portion 51.

As mentioned above, since connecting portion 49 which connects firstconnection portion 41 and second connection portion 51 has a bufferingstructure which can be deformed in the XYZ axis directions, allowance ofthe battery cell at a time of manufacturing or assembling can beabsorbed. Even though a displacement in a relative position betweenfirst connection portion 41 and second connection portion 51, occurs, ata time of using the power supply device, due to swell or expansion bycharging/discharging of the battery cell, external force of impact orvibration, the displacement can be absorbed by the buffering structureof connecting portion 49. Then, this can avoid occurrence of damage,break, or separation in the welding portion, which is caused by the loaddirectly applied to first connection portion 41 or second connectionportion 51. Therefore, the reliability of connecting the battery cellscan be enhanced.

In addition, the intermediate portion of bus bar 40 can be used as adetection terminal for detecting the intermediate potential. Especially,in a case where the lithium ion secondary battery is used as the batterycell, in order to manage a battery state precisely, detecting theintermediate potential is carried out. For this purpose, it is necessarythat terminals for detecting the intermediate potential are connected.The intermediate portion having the buffering structure (impactabsorbing structure) can be also used as a member for connecting theterminal of detecting the intermediate potential.

(Cutout for Connecting the Terminal)

In the example of FIG. 4, a cutout for connecting the terminal is formedat second intermediate portion 55 of one of the intermediate portions.In this example, an area (=square measure=size) of second intermediateportion 55 is larger than an area of first intermediate portion 45.Therefore, the cutout for connecting the terminal can be easily formedat a part thereof. The cutout for connecting the terminal is connectinghole 58 which is opened at second intermediate portion 55. Connectinghole 58 has a circular shape in a plan view in the example of FIG. 4.Connecting hole 58 having the circular shape, can be easily fixed byscrewing the terminal for detecting the intermediate potential, and thena contacting area to the terminal can be large to reduce a contactresistance. The member for connecting the terminal is not limited tothis configuration. The cutout for connecting the terminal can has arectangular shape, an enlonged circular shape, or an elliptic shape. Thecutout is not limited to the hole shape, and can be a recess or thelike.

(Thin Area 61)

Bus bar 40 has a welding area, that is, a joining area, for being laserwelded to the electrode terminal 2 of the battery cell. Concretely, asone exemplary embodiment of the joining area, first connection portion41 and second connection portion 51 each partially have a thin area 61whose thickness is thinner than a thickness of the other area. As oneexample, an enlarged plan view illustrating thin area 61 of firstconnection portion 41, is shown in FIG. 6.

(Open Window 62)

Open window 62 is opened, formed at a part of thin area 61. At a time oflaser welding, the laser beam is irradiated to the upper surface of thinarea 61 which is stacked on, is disposed on, closely contacts, joiningsurface 2B of electrode terminal 2. Then, thin area 61 is welded tojoining surface 2B, while thin area 61 is melted with joining surface 2Bby the laser beam's penetrating. At this time, it is necessary toprecisely position bus bar 40 and electrode terminal 2. Therefore, asshown in the enlarged plan view of FIG. 6, projecting portion 2A ofelectrode terminal 2 is exposed from open window 62, while they are usedas the guide for positioning bus bar 40 and electrode terminal 2relatively. Additionally, they are also used as another guide forpositioning welding location where the laser beam is irradiated. Forexample, projecting portion 2A exposed from open window 62 is detectedby image processing. Then, while this position is regarded as thereference position, scanning position of the laser beam is controlled.Thereby, the joining portion between bus bar 40 and the terminal base ofelectrode terminal 2 is formed.

Open window 62 has a rectangular shape extended in the stacked directionof the battery cells. Open window 62 having the rectangular shape can beformed to have a width bigger than a width of the outer diameter ofprojecting portion 2A of electrode terminal 2. However, preferably, thewidth of open window 62 having the rectangular shape is narrower thanprojecting portion 2A of electrode terminal 2, and also open window 62is formed to be wide, substantially at a center of a longitudinaldirection of open window 62, such that projecting portion 2A can beinserted. While this structure prevents projecting portion 2A from beingincorrectly inserted into the portion of the narrow width, Joiningsurface 2B of the terminal base can be exposed from open window 62located at the both sides of projecting portion 2A. Joining surface 2Bexposed from open window 62, is used for detecting a height of the busbar. The area of open window 62 is suppressed in a small one, and thusan area where it is possible to be laser welded, can be secured by thepart, to improve connecting strength. In the example of FIG. 6, widewidth area 63 having a circular arc shape along the circular outer shapeof projecting portion 2A, is formed, at the center of open window 62having the rectangular shape which is long in the longitudinaldirection.

(Shape of Thin Area 61)

Thin area 61 has an enlonged circular shape or an enlonged ellipticshape in the stacked direction of the battery cells. Thus, both ofdownsizing of the bus bar and securing of the strength of laser weldingcan be carried out. This is explained in the following, based on acomparative example shown in FIGS. 7 to 10. Thin area 61 of thecomparative example has a circular shape. As shown in the plan view ofFIG. 7, bus bar 740 of this configuration is welded to electrodeterminal 702 of a battery stacked body where plural sheets ofrectangular battery cells 701 are stacked. At a time of this welding, asshown in a perspective view of FIG. 8, in a state where each of bus bars740 is disposed on electrode terminal 702 of battery cell 701, bus bar740 is pressed from the upper surface thereof, by using jig JG. Then, byscanning the laser beam shown in a sectional view of FIG. 9, bus bar 740is welded to electrode terminal 702. However, in this configuration, asshown in an enlarged plan view of FIG. 10, it is necessary that pressingarea PA pressed by jig JG are provided at the periphery of laser weldingpattern LP. Thus, it is necessary that an area of bus bar 740 becomeslarge by this part. In addition, recently, downsizing or weigh-saving ofthe power supply device is strongly demanded. Especially, in the use fora vehicle, the downsizing is also further demanded from a view point ofthe fuel efficiency. In response to this demand, when theabove-mentioned laser welding is carried out without increasing a sizeof the bus bar, an area capable of being welded becomes small in arelation with disposing space of the jig or an insulating wall, toprevent the welding strength of the bus bar from being improved. Thus,the demand of downsizing and the demand of weigh-saving are opposed, itis difficult to keep both of them.

In this exemplary embodiment, as shown in FIG. 6, thin area 61 is not acircular shape, but an enlonged circular shape or an elliptic shapeenlonged in the stacked direction of battery cells 1, that is, thetransverse direction in the figure, conversely shortened vertically.Pressing areas where bus bar 40 is pressed by jigs JG′ at the time ofwelding, are omitted at the right and left sides in the stackeddirection of battery cells 1, and then the pressing areas are disposedonly in the upper-lower direction, while sandwiching thin area 61. Thus,the space where the jig is disposed in the comparative example, can beused for welding, and then it is possible to increase the joiningstrength by the part correspondingly. As the result, it is unnecessaryto secure a large area in the right and left direction of bus bar 40, tocontribute to the downsizing of the bus bar.

(Decentered Disposition of Open Window 62)

As open window 62 is provided at thin area 61, thin area 61 is dividedsubstantially into two parts, in the vertical direction, that is, in thedirection of the short side in the elliptic shape. In the example of theplan view of FIG. 6, open window 62 is disposed, substantially at thecenter in the direction of the short side of the elliptic shape of thinarea 61, in other word, the direction (the upper-lower direction in thefigure) crossing the stacked direction of battery cells 1. Preferably,as shown in a modified example of FIG. 12, open window 62 is disposed ata location decentered in the direction away from first connectionbending area 42 in the direction of the short side. Thus, an area oflaser welding pattern LP which is scanned with laser light, can be keptlarge in first connection bending area 42 side. As mentioned above, therelative misalignment between first connection portion 41 and secondconnection portion 51 is absorbed by the deformation of connectingportion 49 in bus bar 40. In terms of first connection portion 41, firstconnection portion 41 is coupled to first bending portion 43 throughfirst connection bending area 42. When battery cells 1 adjacentlydisposed are relatively misaligned and the positions of electrodeterminals 2 displace, bus bar 40 tries to absorb such a displacement. Inother words, first connection bending area 42 bends. Bending of firstconnection bending area 42 is applied to a direction where firstconnection portion 41 is separated from joining surface 2B of electrodeterminal 2. In other words, there is the following tendency. In thinarea 61 as the joining area of first connection portion 41, more stressis applied to a side near first connection bending area 42. Then, inorder to more strongly weld the portion which is apt to receive such astress, open window 62 is disposed at the location decentered in thedirection away from first connection bending area 42 in thin area 61, soas to weld in a large area at the side near first connection bendingarea 42. As the result, in the upper and lower thin areas at the longsides in the elliptic shape of the thin area, the upper side area nearfirst connection bending area 42 is larger than the lower side area awaytherefrom. Therefore, laser welding is continuously carried out in alarge area, to easily perform stronger joining strength. Then, problemsof separation, break in this portion can be avoided, and an improvementof the reliability of laser welding connecting the battery cells can becontributed.

Additionally, from the above-mentioned view point, it is preferable thatthe elliptic shape of thin area 61 has a linear area in first connectionbending area 42 side. In circular thin area 761 of the comparativeexample shown in FIG. 10, when a stress is applied to a direction wherefirst connection portion 41 is separated as mentioned above, the stressis concentrated at a nearest point CP to first connection bending area42. When the stress is concentrated at one point, the possibility of thebreak or the like is increased. Then, as shown in FIGS. 12 and 6, theelliptic shape of thin area 61 has the linear area at the side nearfirst connection bending area 42, and the stress can be received at, nota point, but a line, and then the durability is increased, to contributethe improvement of the reliability. From this view point, it ispreferable that the elliptic shape of thin area 61 has a track shapewhere the long sides are respectively of linear shapes. Alternatively,as shown in a modified example of FIG. 13, the elliptic shape of thinarea 61 can have a linear shape only at the side near first connectionbending area 42. Further, as shown in FIGS. 16 and 17 described below,the rectangular shape with corners cut can be used. The elliptic shapeused in this specification includes and means these shapes. In addition,from the view point of stress concentration, the joining portion is notnecessarily limited to the elliptic shape. As long as the linear joiningportion is provided in a direction transverse to the separatingdirection, when big force is applied to the bus bar, the break of thebus bar can be prevented. Therefore, for example, as shown in anotherexemplary embodiment illustrated in FIG. 16, the laser beam can bescanned so as to form a plurality of linear joining portions extended ina direction of the long diameter of thin area 61. As mentioned above,since the stress is concentrated at the side near first connectionbending area 42, preferably, a region where the linear joining portionis formed at the side near first connection bending area 42, is largerthan a region where a linear joining portion is formed at a side awayfrom first connection bending area 42.

As mentioned above, the elliptic joining portion is formed in theelliptic shape such that the short diameter direction is at connectingportion 49 side, or the linear joining portion is formed at connectingportion 49 side. Therefore, the joining strength can be enhanced againstthe stress which is applied in the direction where first connectionportion 41 is separated. Since the joining strength is enhanced, it ispossible that the bus bar is configured of an inexpensive metal board.Conventionally, from the view point of the reliability of the joiningstrength, the bus bar used in the laser welding is made of a cladmaterial. Recently, as a battery cell, a lithium ion secondary batteryof high capacity has been spread. In this lithium ion secondary battery,generally, the positive electrode is made of aluminum, and the negativeelectrode is made of copper. When these lithium ion secondary batteriesare connected each other in series by the bus bars, it is necessary,that the positive electrode made of aluminum in one of the lithium ionsecondary batteries, is connected to the negative electrode made ofcopper in another of the lithium ion secondary batteries by the busbars. Thus, metal materials of the positive and negative electrodes aredifferent. However, When these different kinds of metals are joined eachother by laser welding, the intermetallic compound is made, and thenthere is a problem that the mechanical strength at the joining portionis decreased. In order to avoid this, the bus bar is made of a cladmaterial which is joined by specially rolling the copper plate andaluminum plate. By using this clad material as a bus bar, aluminumplates are contacted in the positive electrode, and copper plates arecontacted, to prevent the intermetallic compound from being made. Then,laser welding of the high reliability can be obtained. However, there isa problem that the bus bar made of the clad material is expensive. Oncontrast, by contriving jig JG′ above-mentioned, jigs are not disposedin the stacked direction of battery cells 1, as shown in FIG. 11. Thus,the thin area capable of being welded is increased by the partcorrespondingly, and the joining strength is secured by enlarging thearea of laser welding. As a result, without a clad material, the bus barconfigured of only one metal plate (=board), can be utilized, to largelyreduce costs. In this example, the bus bar is made of inexpensivealuminum, but it can be made of copper.

Further, depending on the need, plating can be given to the surface ofthe electrode terminal. When the negative electrode terminal made ofcopper is joined with the bus bar made of aluminum as a different metaljoining, a local cell by a potential difference is formed, and thegalvanic corrosion (different metal contact corrosion) is caused. Then,there is a possibility that the strength is decreased and the electricresistance is degraded. Therefore, nickel plating is given to thesurface of the negative electrode terminal made of copper, to enhance aneffect of corrosion prevention.

Further, there is a merit that laser welding can be done by nickelplating. Since the surface of the electrode terminal made of copper isglossy, the irradiating laser beam is reflected on its surface, andheating and melting by the laser beam irradiation is difficult. Oncontrast, by giving nickel plating to the surface, the nickel platinglayer is melted in advance due to the difference of the melting pointsof nickel and copper, and copper is easily melted. As a result, thegloss of the surface of copper is lost, and the laser beam is notreflected and is absorbed relatively. Since melting is promoted, it ispossible that laser welding progresses smoothly.

(Manufacturing Method of the Power Supply Device)

As a manufacturing method of the power supply device, a method where busbar 40 is laser welded to electrode terminal 2, is explained in thefollowing. The battery stacked body where the plural sheets of batterycells 1 having positive and negative electrode terminals 2 at onesurface are stacked, is prepared. Then, bus bar 4 is disposed, whilebeing positioned on electrode terminals 2 of adjacent battery cells 1.Further, by scanning the laser beam on the thin area, bus bar 40 iswelded and joined to electrode terminal 702.

(Laser Welding Pattern LP)

Next, thin area 61 of the elliptic shape shown in FIG. 6 is scanned withthe laser beam by using a scanning pattern, that is, laser weldingpattern LP shown in a plan view of FIG. 14. As shown by the bold linesin this figure, in the example where open window 62 is formedsubstantially at the center of thin area 61, the laser beam is scannedaccording to the elliptic shaped pattern so as to surround the peripheryof open window 62 by many times. Thereby, the elliptic joining portionwhich joins bus bar 40 and the terminal base of electrode terminal 2 inthe elliptic shape, is formed.

As shown in the plan view of FIG. 12, open window 62 is disposed at alocation decentered toward lower such that first connection bending area42 side is kept large. As shown in an enlarged plan view of FIG. 15, thelaser beam is scanned in a circular arc shape such that the laser beamis rotated around the periphery of open window 62. In addition, at theupper large area, the laser beam is scanned so as to reciprocatelaterally, to enable to efficiently scan the laser beam. As the order ofscanning the laser beam, firstly the laser beam is scanned in a spiralshape from inside toward outside. After scanning in a ring shape havinga predetermined width is finished, at the upper side of open window 62,the laser beam is scanned by the linear reciprocatory scan in thelateral direction. When the laser beam arrives at one of both ends ofthe reciprocatory scan, the laser beam is moved from bottom to top, torepeat the reciprocatory scan. Alternatively, in stead of moving at theone of both ends, the laser beam can be scanned in a zigzag shape.

In the above examples, the laser beam is also scanned at the right andleft sides of open window 62, that is, spaces between open window 62 andthin area 61 in the stacked direction of battery cells 1, to secure thejoining area (=square measure=size) welded by laser. According to thisconfiguration, the joining area is increased, and the joining strengthis enhanced. However, the present invention is not limited to thisconfiguration. Only the upper and left sides of the open window can belaser welded without laser welding the right and left sides of the openwindow. Especially, in a case where there is almost no thin area 61 atthe right and left sides of the open window as the result of furtherdownsizing the bus bar, or in a case where it is difficult to preciselycontrol the scan of the laser beam due to a scanning accuracy of thelaser beam, the scan by the laser beam at these portions can be omitted,to enable cycle time to be shortened while work steps are simplified.Such a example is shown in FIG. 16 or 17 as a modified example. In theexample of FIG. 16, the laser welding is carried out by thereciprocatory scan in the lateral direction at the upper and left sidesof open window 62. Especially, this scan pattern is effective, when thinarea 61 is near a rectangular shape rather than a circular shape.Alternatively, as shown in FIG. 17, the laser beam is scanned in aspiral shape at the upper and left sides of open window 62. Then, thelaser welding can be carried out, so as to cover these areas.

As mentioned above, the thin area is an area for laser welding to theelectrode terminal. However, it is not necessary to weld at the wholethin area, and a part of the thin area may not be welded. Depending on ascan speed of the laser beam, a required connecting strength, or thelike, it is enough to laser weld a necessary area (=square measure=size)of the thin area. Such a exemplary embodiment is also within the scopeof the present invention.

The power supply device described above can be used for avehicle-mounted power supply. Examples of a vehicle having a powersupply device mounted include electric vehicles such as hybrid cars orplug-in hybrid cars driven by both an engine and a motor, orelectric-motor driven automobiles such as electric automobiles onlydriven by a motor. The power supply device can be used for powersupplies of these vehicles.

(Power Supply Device for Hybrid Automobile)

FIG. 18 shows an example in which a power supply device is mounted on ahybrid car driven by both an engine and a motor. Vehicle HV equippedwith a power supply device that is shown in this drawing includes:engine 96 and motor 93 for travel that make vehicle HV travel; powersupply device 100 for supplying power to motor 93; and power generator94 for charging the battery in power supply device 100. Power supplydevice 100 is connected to motor 93 and power generator 94 via directcurrent (DC)/alternating current (AC) inverter 95. Vehicle HV travels byboth of motor 93 and engine 96 while charging and discharging thebattery of power supply device 100. Motor 93 is driven when the engineefficiency is low, for example during acceleration or low-speed travel,and makes the vehicle travel. Motor 93 receives power from power supplydevice 100 and is driven. Power generator 94 is driven by engine 96 oris driven by regenerative braking when the vehicle is braked, and thebattery of power supply device 100 is charged.

(Power Supply Device for Electric Car)

FIG. 10 shows an example in which a power supply device is mounted in anelectric car traveling only by a motor. Vehicle EV equipped with a powersupply device that is shown in this drawing includes: motor 93 fortravel that makes vehicle EV travel; power supply device 100 forsupplying power to motor 93; and power generator 94 for charging thebattery in power supply device 100. Motor 93 receives power from powersupply device 100 and is driven. Power generator 94 is driven by energywhen regenerative braking is applied to vehicle EV, and the battery ofpower supply device 100 is charged.

A power supply device, a vehicle using this, or a bus bar according tothe present invention can be suitably used as power supply devices ofplug-in hybrid vehicles that can switch between the EV drive mode andthe HEV drive mode, hybrid electric vehicles, electric vehicles, and thelike. The power supply device can be appropriately used for thefollowing applications: a backup power supply device mountable in a rackof a computer sever; a backup power supply device used for wireless basestations of mobile phones; a power source for storage used at home or ina factory; an electric storage device combined with a solar battery,such as a power source for street lights; and a backup power source fortraffic lights.

The invention claimed is:
 1. A power supply device comprising: aplurality of battery cells each having a positive electrode terminal anda negative electrode terminal; and a bus bar which connects theelectrode terminals facing each other in the battery cells adjacentlydisposed among the plurality of battery cells, wherein the bus barincludes: a first connection portion which is connected to the electrodeterminal of one of the battery cells; a second connection portion whichis connected to the electrode terminal of another of the battery cells,and is disposed substantially in parallel to the first connectionportion; a first intermediate portion which is continuous from the firstconnection portion through a first bending portion that is bent from thefirst connection portion, the first intermediate portion being disposedsubstantially in parallel to the first connection portion; and a secondintermediate portion which is continuous from the second connectionportion through a second bending portion that is bent from the secondconnection portion, the second intermediate portion being disposedsubstantially in parallel to the second connection portion, wherein thefirst intermediate portion and the second intermediate portion areconnected in a continuous manner by a third bending portion having aU-shaped cross-section, wherein the bus bar has an overall U-shape inplan view with a gap between the first connection portion and the secondconnection portion, and wherein the U-shaped cross-section of the thirdbending portion protrudes toward the battery cell.
 2. The power supplydevice according to claim 1, wherein an extent of an area of the secondintermediate portion is larger than an extent of an area of the firstintermediate portion, and a connecting cutout for connecting a terminalis formed at the second intermediate portion, wherein the connectingcutout is a hole connecting a detection terminal configured to detect anintermediate potential.
 3. The power supply device according to claim 2,wherein the connecting hole has a circular shape.
 4. The power supplydevice according to claim 1, wherein the positive electrode terminal andthe negative electrode terminal are made of different kinds of metals,the metal of the bus bar is the same kind of the metal as one of thedifferent kinds of metals, and one of the first connection portion andthe second connection portion, connected to the electrode terminalhaving the same kind of the metal, partially has a narrow area having awidth narrower than that of the other of the first connection portionand the second connection portion, wherein the first bending portion andthe second bending portion have different widths from each other.
 5. Thepower supply device according to claim 4, wherein one of the firstbending portion and the second bending portion which has a widthnarrower than that of the other of the first bending portion and thesecond bending portion is bent from the one of the first connectionportion and the second connection portion which partially has the narrowarea.
 6. The power supply device according to claim 1, wherein the firstconnection portion and the second connection portion each partially havea region that has a lesser relative thickness than another nearbyregion.
 7. The power supply device according to claim 1, wherein the busbar is one sheet of a bended metal board.
 8. The power supply deviceaccording to claim 1, wherein a surface of at least one of the positiveelectrode terminal and the negative electrode terminal is plated with aplating metal different from the at least one of the positive electrodeterminal and the negative electrode terminal.
 9. The power supply deviceaccording to claim 8, wherein the at least one of the positive electrodeterminal and the negative electrode terminal is made of copper, theplating metal is nickel, the bus bar is made of aluminum.
 10. A vehiclecomprising the power supply device according to claim
 1. 11. A bus barfor connecting electrode terminals of a pair of battery cells,comprising: a first connection portion which is connected to theelectrode terminal of one of the battery cells; a second connectionportion which is connected to the electrode terminal of another of thebattery cells, and is disposed substantially in parallel to the firstconnection portion; a first intermediate portion which is continuousfrom the first connection portion through a first bending portion thatis bent from the first connection portion, the first intermediateportion being disposed substantially in parallel to the first connectionportion; and a second intermediate portion which is continuous from thesecond connection portion through a second bending portion that is bentfrom the second connection portion, the second intermediate portionbeing disposed substantially in parallel to the second connectionportion, wherein the first intermediate portion and the secondintermediate portion are connected in a continuous manner by a thirdbending portion having a U-shaped cross-section, wherein the bus bar hasan overall U-shape in plan view with a gap between the first connectionportion and the second connection portion, and wherein the U-shapedcross-section of the third bending portion protrudes toward the batterycell.